Vapor generator having welded panel construction



R. U. SHEIKH Oct. 19, 1965 VAPOR GENERATOR HAVING WELDED PANEL CONSTRUCTION 4 Sheets-Sheet 1 Filed May 9, 1962 INVENTOR:

RAMSEY U. SHE IKH FIG.

Oct. 19, 1965 R. u. SHEIKH 3,212,479

VAPOR GENERATOR HAVING WELDED PANEL CONSTRUCTION Filed May 9, 1962 4 Sheets-Sheet 3 (law ATTORNEY R. U. SHEIKH Oct. 19, 1965 VAPOR GENERATOR HAVING WELDED PANEL CONSTRUCTION Filed May 9, 1962 4 Sheets-Sheet 4 MIVENTOR RAM-5E Y0. SHE/Kb W 86% ATTORNE FIG. a

FIG. 7

a... p a. a o lo mmm mam United States Patent 3,212,479 VAPOR GENERATOR HAVING WELDED PANEL CONSTRUCTION Ramsey U. Sheikh, Avon, Conn., assiguor to Combustion Engineering, Inc., Windsor, Conn-n, a corporation of Delaware Filed May 9, 1962, Ser. No. 193,551 Claims. (Cl. 122-510) This invention relates to improvements in vapor generators. More particularly, the invention relates to the construction of vapor generators of the water wall type wherein the boiler bank is located in an elevated position within the generator and to the means for supporting the boiler bank in said elevated position.

In vertically oriented units of the present type the height of the combustion chamber is quite large in relation to the boiler bank, conventional units often being designed with a combustion chamber height which is twice that of the boiler bank. Due to the difference in length of the tubes which define the combustion chamber and those which define the boiler bank, there is created the problem of unequaled thermal expansion of the tubes. Such unequal elongation of the tubes can be very harmful in that tremendous stresses are established therein which could ultimately result in failure of the tubes and cessation of operation of the generator. To overcome this problem it has heretofore been necessary to surround the generator with a heavy steel supporting structure from which both the combustion chamber and the boiler bank could be suspended so as to permit all of the parts to expand downwardly when they are heated. Having to provide heavy steel supporting structure capable of suspending both the walls of the combustion chamber and the boiler bank, greatly increases the cost of such vapor generating units. In a typical construction the cost of such steel structure amounts to a substantial portion of the total cost of the unit.

By means of the present invention there is provided a generator design which obviates the need to suspend the unit from above and concomitantly, the need for such separate support structure, the entire unit being completely floor supported. Floor supporting of the unit is permitted because the entire vapor generator is designed for upward thermal expansion. Such expansion is provided by the fact that the boiler bank in the instant vapor generator is supported in its elevated position upon the side walls of the unit.

Furthermore, in vapor generator units of the Water wall type a considerable portion of the cost is realized in the form of erection costs. Such costs are attributed to a great extent to the time and manpower involved in assembling the component parts and erecting them in the field. The present invention contemplates fabricating the walls of the combustion chamber in the shop, the walls comprising a number of panels each of which consists of a plurality of united, parallel tubes. The panels are transported to the erection site where they are merely erected and joined together in end-to-end relation by means of a welding operation thereby forming a continuous, rigid, box-type structure.

By fabricating the walls as panels there is no longer a need to erect and weld each of the pressure parts individually in the field as was heretofore the case. By uniting a number of the tubes into panels each tube can be cut, fitted and welded in place in the shop. Any error that arises can be rapidly and expeditiously corrected using equipment that is too cumbersome to be employed in the field. The panels can then be transported to the construction site where assembling them into the vapor generator involves only a minimum amount of field welding.

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The present vapor generator design also gives rise to a novel configuration of the combustion chamber as applied to stoker firing. The rear wall of the unit is oifset to form an internal projection which overlies a substantial portion of the firing unit. The lower leg of the projection is in clined toward the upper front corner of the chamber which heretofore had been a point of stagnancy within similar combustion chambers. This leg serves as a bafile to direct the gases of combustion emitted from a firing unit into this portion of the chamber thus permitting utilization of all of the available heating surface within the chamber. The contour also results in a very turbulent lower chamber and a passageway which effects a smooth change in direction of the gases before they enter the superheater and the boiler bank. The nose-like offset additionally provides a means for shielding the bends of the superheater from the direct radiation of the fuel bed. This expedient results in a superheater having semiradiant characteristics thereby providing more uniform superheat over a wide range of boiler loads. Still further, the lower leg of the projection is weldedly attached to the spaced side wall panels that support the boiler bank. Therefore, the rear wall of the unit serves as a strengthening tie between the side Wall panels reducing their unsupported height and thereby enhancing their columnar strength.

Therefore, it is a general object of the present invention to provide a vertically elongated vapor generator having the boiler bank located in an elevated position therein which may be completely floor supported thus eliminating the need for expensive suspension structure.

It is also an object of the present invention to provide a vapor generator wherein the costs of erection are materially reduced by forming the component parts into panels.

A still further object of the present invention is to provide a combustion chamber configuration wherein all of the available heating surface is utilized in the creation of vapor thus effecting an increase in generator efliciency.

Additional objects and advantages will become apparent from the illustrative description which follows when read in conjunction with the appended drawings in which:

FIG. 1 is a vertical section of a vapor generator incorporating the instant invention;

FIG. 2 is a rear view of a portion of the vapor generator shown in FIG. 1;

FIG. 3 is a front view of a portion of the generator shown in FIG. 1;

FIG. 4 is an enlarged view of a portion of the side wall panels employed in the instant generator;

FIG. 5 is a cross sectional view taken along line 5-5 in FIG. 1;

FIG. 6 shows a typical section of the lower portion of a generator wall;

FIG. 7 is a plan section taken along line 7-7 of FIG. 1; and

FIG. 8 is a cross sectional view of the instant generator taken along line 88 in FIG. 1.

Referring to FIG. 1 there is shown a vapor generator unit 10 which embodies the present invention. This unit is of the vertically oriented type having an output rating of from 100,000 to 250,000 pounds of vapor per hour although the invention is not limited to generators of this a boiler bank portion 12 and a firing unit 13. A superheater 14 may be interposed between the combustion chamber 11 and the boiler bank 12. Hot gases generated by the firing unit 13 flow through the combustion chamber 11 and then pass through the superheater 14 and boiler bank 13 through opening 15 in the rear of the unit before entering the rear gas pass (not shown) which houses the auxiliary generator equipment. A nose projection 16 extends into the combustion chamber 11 and forms a bafile means to aid in directing the flow of gases through the unit and a means to shield the bends of the superheater tubes from the effects of radiant heat.

The vapor generator is of substantially rectangular cross section and comprises the vertically extending combustion chamber 11 that is defined by fiuid cooled, tubulous walls indicated as being front wall 17, a pair of spaced walls 18 and rear wall 19. The structure is closed at the top -by roof 20, which is formed as an extension of the front wall 17, and at the bottom by a foundation The vapor generator 10 also includes boiler bank portion 12 that laterally adjoins and communicates with the upper portion of the combustion chamber 11. The boiler bank 12 comprises an upper drum 22, a lower drum 23 and a plurality of laterally spaced rows of vertically extending substantially C-shaped boiler tubes 24 that interconnect the two drums. The side walls 18 of the vapor generator are formed by a plurality of vertically extending, fluid conducting tubes 26 that connect with lower headers 28 at the bottom of the unit and upper headers 28' at the top. As shown in FIGURE 4, the ends of the tubes 26 are swaged into accommodating apertures 29 in the headers and, as best described with reference to FIGURES 4 and 7, the tubes 26 are arranged in vertically parallel, spaced relation with the spaces therebetween being welded at least in the area of the gas enclosure by metallic strips 27 which are welded to adjacent tubes thereby giving rise to a continuous metallic wall surface hereinafter referred to as a membranous wall. Front wall 17 is similarly formed as a membranous wall with the tubes 26 thereof connecting at their bottom ends to lower front wall headers 36 that extend across the front 'of the unit between the side walls 18. The tubes 26 of this wall, however, are not connected to headers at their top but instead are offset to extend longitudinally across the top of the combustion chamber 11 and connect with the upper drum 22 to thus form the roof 20. As shown in FIGURE 1, the lower end of front wall 17 is inwardly offset so as to accommodate the structure 32 which is fixedly mounted to headers 30 by means of attaching plate 33 and which is operatively associated with the structure 63.

Elongated apertures 34 are provided in the rear portion of the roof in order to accommodate the superheater inlet and outlet lines, 35 and 36 respectively. These openings are formed by offsetting alternate roof tubes 31 both laterally and vertically so that they overlie the adjacent tubes 31. Between the so-formed double rows of tubes 31 and 31 the superheater inlet and outlet lines 35 and 36 are located, uniting the superheater 14 with the inlet and outlet headers 38 and 39 respectively. Crown plates 40 which are apertured to accommodate the superheater inlet and outlet lines 35 and 36 straddle the elongated apertures 34 formed in the roof 20 and are welded to the roof tubes 31' so as to seal the gases within the generator. Sealing plates 69 which are attached to the roof tubes 31' in front of and behind the crown plates 40 complete the seal in this area of the unit.

The body of the generator 10 is completed by the rear wall 19 which is also formed as a membranous wall, the lateral ends of the wall being welded to the adjacent ends of the opposed side walls 18 as shown in FIG. 7 to provide a continuous gas enclosure structure. The tubes 26 that form the rear wall 19 extend from lower rear wall headers 43 to the upper durm 22 but are offset just below the boiler bank 12 to form a nose portion 16. The lower leg 41 of the nose portion 16 is inclined upwardly toward the upper front corner 42 of the generator and serves as a baffle to direct the gases of combustion toward that area of the unit which, in similar units, had been an area of stagnation wherein little gas circulation took place thus rendering the tubes located in this area of little use for the purpose of heat transfer. By means of the disclosed structure the combustion gases generated by the firing unit 13 are caused to flow upwardly to heat all parts of the heating surface which are exposed thereto and to effect a smooth change of direction in flowing through the superheater 14 and the boiler bank 12.

While the tubes 26 which form the rear wall 19 extend from the lower rear wall header 43 to the upper drum 22, the metal strip 27 which unites the tubes terminates at a point, indicated as 44, adjacent the lower drum 23. Above this point 44 the tubes are rearwardly and laterally offset and exist in spaced relation thus forming screen tubes 45 for the boiler bank 12 through which the combustion gases are capable of passing.

By forming the rear wall 19 in this fashion several important accomplishments are achieved. First, the rear wall 19, by means of the nose portion 16, serves, as mentioned above, to enhance gas circulation within the vapor generator unit. Secondly, as shown in FIG. 1 the superheater tubes extend downwardly to a point closely adjacent the upper leg 46 of the nose 16, thus permitting the nose 16 to shield the tube bends 14 from the radiant heat emitted from the fuel bed. Shielding the superheater 14 from much of the radiant heat of combustion is desirable in order to limit the amount of radiant heat imparted to the superheater tubes relative to the convection heat such that little change in the superheat characteristics will be realized over expansive load changes upon the generator.

And thirdly, since the rear wall 19 is welded to each of the side walls 18, the nose portion 16 of the wall serves as a structural beam to stiffen the generator walls and thus render the generator more sturdy in the area of the boiler bank 12 where the stress upon the walls of the unit will be most concentrated. The rear wall 19 is weldedly connected to the side walls 18 along the vertical portion from just above the stoker grate 63 to a level spaced below the upper headers 48 of the rearwardmost side wall panel which supports the boiler bank. The welded connection between the rear wall 19 and the side walls 13 continues along the lower leg 41 of the nose portion 16 to the point 44. In this manner the rear wall 19 serves as a stiffening beam attached to the panels which support the boiler bank intermediate their upper headers 48 and their lower headers 28 thereby reducing the unsupported height of the panels.

In the construction of the instant vapor generator the walls 17-19 and roof 20 are formed as prefabricated, tube-bearing panels that are assembled in the shop and thereafter transported to the boiler site where they are erected and welded together by means of field welds to form a box-like structure having a continuous metal surface forming the gas enclosure. Typical of such panels are the side wall panels shown in FIGURE 1 as comprising a lower header 28, an upper header 28 that is in vertical alignment with, but spaced from, the lower header and a plurality of vertically parallel tubes 26 that lie in a common plane and whose ends are connected to each of the headers. The tubes 26 that comprise each panel are weldedly united in side-by-side relation by means of the metal strips 27 that fill the spaces between the tubes in accordance with the teaching of US. Patent No. 2,719,- 210 to Chapman. The length of the headers and the number of tubes that comprise each panel are dictated by transportation requirements. For example, the width of such a panel may be about four feet so as to be conveniently shipped to the boiler site. The front wall 17 and rear wall 19 are similarly constructed as panels, but in these walls the tubes extend from lower headers 30 or 43 at their bottom to connect directly with the upper drum 22 in the case of the front wall 17 and with the lower drum 23 in the case of the rear Wall 19. The panels are erected at the boiler site in side-by-side relation and field weldsare applied to connect the end edges of adjacent panels to thereby form a vapor generator of rectangular 5. section whose Walls are formed of a continuous metal surface as shown in FIGURES 7 and 8.

Elimination of the heavy steel supporting structure ordinarily required for vapor generators of comparable size is provided in accordance with the invention by the fact that the boiler bank 12 is vertically supported by the generator walls thus permitting all vertical thermal expansion of the generator parts to occur in the upward direction. As shown in FIGURES l and 2, the boiler bank 12 is supported upon, and traverses the top of the rearwardmost side wall panels, indicated as 73. These panels 73 comprise the same membranous wall structure employed in the formation of the remainder of the vapor generator gas enclosure and include vertically straight tubes 26 that extend between lower side wall headers 28 and upper rear panel headers indicated as 48 but are, however, shorter in height than the remainder of the tubes 26 that form the side walls 18 by an amount that is substantially equal to the height of the boiler bank 12 such that the upper drum 22 is located at approximately the same elevation as the upper side wall headers 28. The means for mounting the boiler bank 12 upon the headers 48 comprise a pair of drum saddles 47 which are each secured to one of the headers and are adapted to engage the lower drum 23 adjacent each of its ends. The drum saddles 47 each include a bracket member 49 having its upper edge shaped to receive the lower drum 23 and its lower edge shaped to be mounted upon the header 48. Welds are applied between the drum 23 and saddles 47 and also between the base of the saddles and the header 48 so as to secure the mounting.

That the boiler bank 12 can be supported upon the side walls 18 of the unit in this manner is accomplished by the fact that the side wall panels 73 that mount the boiler bank are rendered sufficiently structurally sturdy to withstand the stresses developed by the combined weight of the drums 22 and 23 and boiler tubes 24 that comprise the boiler bank. Strengthening the side wall panels to perform this function is accomplished by several individual factors. First, the tubes are straight thus providing them with a greater amount of columnar strength than were they to be shaped otherwise. Secondly, the tubes that form the panels 73 are all weldedly united in vertically parallel relation thus forming the tube panel as a structural support member. Thirdly, columnar loading of the tubes is insured by the fact that the lower drum 23 which supports the weight of the remainder of the boiler bank 12 is mounted upon the upper rear panel headers 48 in a manner such that the boiler bank load is transferred to the rearwardmost side wall panel 73 as substantially true compressive loads which the tubes 26 can accommodate due to the columnar strength of the tube panels. And lastly, to enhance the columnar strength of the boiler bank-mounting panels 73 the rear wall 19 of the unit is formed as a structural member in that area that overlies the grate 63 and lies in a plane that intersects the planes of the rearwardmost side wall panels 73 intermediate their upper and lower ends and is weldedly attached thereto, thereby reducing the unsupported height of the panels.

Communicating with the lower drum 23 are a plurality of tubes 52 which form a major portion of the downcomer system of the unit. These tubes are located externally of the body of the generator unit, being protected from the gases contained therein by the walls thereof and connect with the various lower headers 28, 30 and 43 that supply the tubes 26 with vaporizable liquid. As shown in FIGS. 1, 2 and 3 the downcomer tubes 52 are positioned as close as possible to the unit walls, 17-19, being literally wrapped around the walls and in communication with the headers which form the lower portion of the walls.

By providing such a downcomer system the amount of insulation required for completely insulating the generator unit is considerably reduced. Heretofore, it had been the practice to locate the downcomer tubes 52 outside of the surface of the generator and of its insulation, thus requiring the downcomer tubes to be completely surrounded by insulating material. In the present design, the tubes are maintained closely adjacent the walls of the generator as shown in FIGS. 1 and 6. Since the tubes are protected from the gases within the combustion chamber 11 by the tube-bearing walls, the amount of heat to which the downcomer tubes 52 are exposed never exceeds the temperature of the fluid carried by the water wall tubes 26, i.e., saturation temperature. Therefore, it is not necessary to insulate the downcomer tubes separately, the insulation 70 for the generator 10 being merely extended to cover the outside of the downcomer tubes 52. An outer lagging 71 formed of aluminum or steel sheeting is applied to the insulation 70, completely covering the unit; thereby protecting the insulation from the harmful eifects of its environment.

Supporting the vapor generator 10 upon the floor 21 are a plurality of footings 25 located at spaced points about the base. As shown in FIG. 1, two footings are provided beneath each of the two opposed side walls 18, spaced inwardly from each end. The rear footings mount the rearwardmost side wall panels 73 and are positioned directly beneath the boiler bank 12 in alignment with the center lines of the upper and lower drums, 22 and 23. The footings 25 are attached to the lower side wall headers 28, as is shown in FIG. 5, in a manner which permits sliding movement upon expansion of the generator Walls. The top of each footing is provided with support platform 53. A bracket 54 is weldedly attached to the lower side wall header 28 with the base 55 thereof being formed with a smooth under surface in order to readily permit unencumbered sliding of the bracket 54 relative to the footing support platform 53. To further enhance sliding of the bracket a lubricated bearing plate 56 is positioned upon the support platform 53, the latter being provided with shoulders 57 to retain the bearing plate 56 upon the platform. A skirt formed of structural members 58 depends from the bracket base 55 thereby providing a shoulder which surrounds the base 55 to coact therewith in order to prevent overexpansion of the side walls. In effect, the so-formed shoulder arrangement serves to limit the movement between the bracket base 55 and the support platform 53 to insure retention of the base upon the platform. Stifiening ribs 59 may be provided to strengthen the depending structural members 58.

Means are provided to insure lateral movement of the bracket 54 upon expansion of the generator walls. This means provides for direct connection of the bracket 54 with a laterally expanding generator member which imparts the force developed by the thermal expansion directly upon the bracket. The means consists of a pair of expansion tubes 60 which extend across the width of the unit and which interconnect the brackets 54 positioned on opposed footings 25. The expansion tubes 60 have their ends capped by means of plugs 61 and communicate with the overlying header 28 by means of a short nipple 62. The tubes 60 receive heated fluid from downcomer tubes 52, some of which extend to, and connect with, the center of tubes 60. The fluid is delivered back to the circulation system through the nipples 62. Circulation of fluid through the tubes 60 induces thermal expansion thereof with the other generator components. In expanding, the tubes act directly upon the brackets 54 to induce sliding thereof in relation to the footings 25.

Also shown in FIG. 5 is the means employed to seal the bottom of the generator between the grate 63 and the side walls 18 such that gases are prevented from leaking therebetween. The grate frame 63 which extends the full length of the travelling grate is provided with a flanged bracket 64. Attached to the lower side wall headers 28 is a bracket 65 which extends the length of the side wall 18. Each of the brackets 64 and 65 are provided with smooth opposed surfaces such that contact between the two surfaces produces an eificient metal-to-metal seal.

' One of the several strengthening features contained in the instant design is shown in FIG. 4 wherein it can be seen that each of the panel headers 28 and 28' is fluidly isolated from the adjacent headers by means of end plugs 66 which are welded in place. Upon erecting the panels at the construction site a spacer ring 6'] is placed between the adjacent ends of the headers 28 and a circumferential Weld 68 applied to rigidly unite the headers. Joining the headers in this fashion is important for several reasons. Firstly, the continuous, smooth surface formed by filling the gaps between the adjacent headers prevents coal and clinker from lodging in the pockets that would otherwise exist between the headers 28 and the grate 63 thus reducing the chance of clinker damage to the headers. A second reason for joining the headers together is to form a structural beam out of the headers, thereby aiding in uniting the panels into a continuous structural unit to thus stiffen the walls. Thirdly, a continuous header assembly serves to alleviate the expansion stresses which are imposed upon the field welds applied to unite the side wall panels. Such stresses are developed by the action of the expansion tubes 60 upon the panels. These tubes are connected to and act upon only the front and rear side wall panels but not the center panel. By means of the unitary header structure the field welds connecting the middle side wall panels to the front and rear side wall panels are prevented from becoming over-stressed since the headers serve to take up the strain imposed by the expanding expansion tubes 59.

The operation of the vapor generator unit is as follows: Vaporizable liquid is admitted to the upper drum 22 and flows downwardly through those of the boiler bank tubes 24 which are rearwardmost in the boiler bank to the lower drum 23 where it is conducted through downcomer tubes 52 to the lower headers 28, 30 and 43 of the generator walls. The fluid then flows upwardly through the tubes 26 which form the generator walls to the upper headers 28' and 48 extracting heat from the combustion gases that flow upwardly through the combustion chamber 11 and through the boiler bank thereby being transformed into steam which is conducted to the upper drum 22 and thence to the superheater 14 from whence it emerges through superheater outlet header 39 and is conducted to a point of use.

The herein described generator, due to the self-supporting nature of its structure, is cable of maintaining the boiler bank portion in its elevated position without the need of any external support members, therefore all vertical support of the generator 10 comes from the footings 25 which are spaced about its base. Floor supporting the generator enables all thermal expansion in the vertical direction to be undergone upwardly with no undue stress upon the tubes of respective sections because of the differences in their length thereby obviating the need to suspend the generator walls and boiler bank in order to permit expansion of the tubes without the establishment of any undue stress therein. An additional feature of the present generator is a novel baffling arrangement provided by nose 16 which permits utilization of substantially all of the available heating surface to thus increase the thermal efficiency of the unit.

While the instant invention has been disclosed with reference to the particular embodiment contained herein it is to be understood that the present description is intended merely to be illustrative of the inventive concept and is in no way intended to restrict it and that variations and modifications may be made therein without departing from the scope of the invention.

What is claimed is:

1. A bottom supported vapor generating unit arranged for vertical thermal expansion in the upward direction comprising rectangularly disposed front, rear, and laterally opposed side walls including vertically arranged tubes defining a combustion chamber; a boiler bank communicating with said combustion chamber including horizontally disposed upper and lower drums extending laterally of said side walls and a plurality of vertically extending tubes connected at their oppositeends to said drums; support means for supporting said boiler bank upon said side walls including header means uniting the upper ends of the tubes forming a portion of said side walls; drum saddle means supported by said header means mounting said lower drum; and means for bottom S pporting said side walls.

2. A bottom supported vapor generating unit arranged for vertical thermal expansion in the upward direction comprising rectangularly disposed front, rear, and laterally opposed side walls including vertically arranged tubes defining a combustion chamber; a boiler bank communicating with said combustion chamber including horizontally disposed, vertically aligned upper and lower drums extending laterally of said side walls and a plurality of substantially vertically extending tubes connected at their opposite ends to said drums; support means for said boiler bank including a portion of said side walls underlying the ends of said lower drum having their tubes weldedly connected in side-by-side relation; upper and lower header means connecting the upper and lower ends of the tubes of said portion; drum saddle means supported by said upper header means mounting said lower drum and means for bottom supporting said lower header means.

3. A bottom supported vapor generating unit arranged for vertical thermal expansion in the upward direction comprising rectangularly disposed front, rear, and laterally opposed side walls including vertically arranged tubes defining a combustion chamber; a boiler bank communicating with said combustion chamber including horizontally disposed, vertically aligned upper and lower drums extending laterally of said side walls and a plurality of substantially vertically extending tubes connected at their opposite ends to said drums, firing means positioned at the bottom of said combustion chamber; support means for said boiler bank including a portion of said side walls underlying said lower drum having their tubes weldedly connected in side-by-side relation; upper and lower header means connecting the upper and lower ends of the tubes of said portion; drum saddle means Supported by said upper header means mounting said lower drum; said rear wall having its tubes weldedly united in side-by-side relation, the lateral ends of said wall being weldedly connected along its length to said side walls; a portion of said rear wall forming an arch over said firing means, said rear wall portion intersecting and being attached to said portion of said side walls in termediate the upper and lower ends thereof for reducing the unsupported height of said side wall portions; and means located in vertical alignment with said drums for bottom supporting said lower header means.

4. A bottom supported vapor generating unit arranged for vertical thermal expansion in the upward direction comprising rectangularly disposed front, rear, and side walls including vertically arranged tubes defining a combustion chamber; a boiler bank communicating with said combustion chamber including horizontally disposed upper and lower drums extending laterally of said side walls and having their axes in substantially the same vertical plane and a plurality of substantially vertically extending tubes connected at their opposite ends to said drums; metal strips welded to and between the tubes forming said walls thereby rendering said walls structurally rigid and gas impervious; firing means positioned at the bottom of said combustion chamber; support means for supporting said boiler bank including a portion of said side walls underlying the ends of said lower drum and the tubes thereof lying in spaced vertical planes normally intersecting the plane of said drum axes; upper and lower header means connecting the upper and lower ends of the tubes of said side wall portions; drum saddle means supported by said upper header means mounting said lower drum; the lateral ends of said rear wall being weldedly connected along its length to said side walls; a portion of said rear wall forming an arch over said firing means, said rear wall portion lying in a plane normally intersecting the plane of said side wall portions and the endmost tubes of said rear wall portion being weldedly attached to said side wall portions intermediate the upper and lower ends thereof for reducing the unsupported height of said side wall portions; and means located in vertical alignment with said drums for bottom supporting said lower header means.

5. A bottom supported vapor generating unit arranged for vertical thermal expansion in the upward direction comprising rectangularly disposed front, rear, and side walls including vertically arranged tubes defining a combustion chamber; a boiler bank communicating with said combustion chamber including horizontally disposed up per and lower drums extending laterally of said side Walls and having their aXes in substantially the same vertical plane and a plurality of substantially vertically extending tubes connected at their opposite ends to said drums; metal strips welded to and between the tubes forming said walls thereby rendering said walls structurally rigid and gas impervious; firing means positioned at the bottom of said combustion chamber; support means for supporting said boiler bank including a portion of said side walls underlying the ends of said lower drum, the tubes thereof being substantially vertically straight and lying in spaced vertical planes normally intersecting the plane of said drum axes; upper and lower header means connecting the upper and lower ends of the tubes of said side wall portions; drum saddle means supported by said upper header means mounting said lower drum; the lateral ends of said rear wall being weldedly connected along its length to said side walls; a portion of said rear wall forming an arch over said firing means, said rear wall portion lying in a plane normally intersecting the plane of said side wall portions and the endmost tubes of said rear wall portion being weldedly attached to said side wall portions intermediate the upper and lower ends thereof for reducing the unsupported height of said side wall portions; and means located in vertical alignment with said drums for bottom supporting said lower header means.

References Cited by the Examiner UNITED STATES PATENTS 1,859,857 5/32 Whittarn 122235 1,922,599 8/33 Murray 122235 11,998,828 4/35 Armacost l2247 8 2,004,058 6/35 Stillman 122-478 2,016,762 10/35 Yoder l22-255 2,583,599 1/52 Schoessow 122510 2,648,316 8/53 Marshall 122-331 2,655,238 10/53 Langvand 122-494 2,703,559 3/55 Godshalk 122--570 2,764,137 9/56 Koch 122-478 2,852,002 9/58 Sprague 122-333 2,979,041 4/61 Young 122--510 3,003,482 10/61 Hamilton et al. l22478 3,012,548 12/61 Guszmann 122--494 PERCY L. PATRICK, Primary Examiner.

FREDERICK L. MATTESON, JR., KENNETH W.

SPRAGUE, Examiners.

[lNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,212,479 October 19, 1965 Ramsey U, Sheikh It is hereby certified that error appears in the above numbered patent requiring correction and that the said Letters Patent should read as corrected below.

Column 2, lines 63 and 64, for "of this a boiler" read of this size. It consists essentially of a combustion chamber 11, a boiler column 7, line 31, for "59" read 60 Signed and sealed this 5th day of July 1966" (SEAL) Attest:

EDWARD J.'BRENNER ERNEST SWIDER Commissioner of Patents Attesting Officer 

1. A BOTTOM SUPPORTED VAPOR GENERATING UNIT ARRANGED FOR VERTICAL THERMAL EXPANSION IN THE UPWARD DIRECTION COMPRISING RECTANGULARLY DISPOSED FRON, REAR, AND LATERALLY OPPOSED SIDE WALLS INCLUDIONG VERTICALLY ARRANGED TUBES DEFINING A COMBUSTION CHAMBER; A BOILER BANK COMMUNICATING WITH SAID COMBUSTION CCHAMBER INCLUDING HORIZONTALLY DISPOSED UPPER AND LOWER DRUMS EXTENDING LATERALLY OF SAID SIDE WALLS AND A PLURALITY OF VERTICALLY EXTENDING TUBES CONNECTED AT THEIR OPPOSITE ENDS TO SAID DRUMS; SUPPORT MEANS FOR SUPPORTING SAID BOILER BANK UPON SAID SIDE WALLS INCLUDING HEADER MEANS UNITING THE UPPER ENDS OF THE TUBES FORMING A PORTION OF SAID SIDE WALLS; DRUM SADDLE MEANS SUPPORTED BY SAID HEADER MEANS MOUNTING SAID LOWER DRUM; AND MEANS FOR BOTTOM SUPPORTING SAID SIDE WALLS. 